Partial all-optical signal processing method and system for phase-sensitive optical time domain reflectometer

Abstract

The invention discloses a partial all-optical signal processing method and system for a phase-sensitive optical time domain reflectometer. The partial all-optical signal processing method comprises the following steps: acquiring a backward Rayleigh scattering signal; dividing the amplified and filtered backward Rayleigh scattering signal into at least two paths of optical signals according to a certain proportion; delay operation is carried out on one path of optical signals, derivation operation is carried out on other paths of optical signals, and it is ensured that all paths of optical signals are synchronous; performing synchronous photoelectric detection on each path of optical signal subjected to derivation and delay operation to obtain the optical power of each path of optical signal; determining the derivative of the phase to be demodulated according to the optical power of each path of optical signal; and processing the derivative of the phase to be demodulated based on Fourier transform to obtain frequency domain information of the phase. In the DAS signal processing process, partial all-optical signal processing replaces a traditional all-electric-domain data processing scheme, and the data processing speed can be remarkably increased; and the system also has the advantages of strong anti-electromagnetic interference capability, strong environmental adaptability and the like.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber sensing technology and relates to the processing of distributed optical fiber sensing signals, and in particular to a partial all-optical signal processing method and system for a phase-sensitive optical time domain reflectometer. Background Art

[0002] Phase-sensitive optical time-domain reflectometry (Φ-OTDR) systems are used as distributed fiber optic sensors, capable of real-time monitoring of tiny disturbances along the optical fiber, such as temperature changes, strain, and vibration. These systems provide effective solutions for monitoring needs in various complex environments and are widely used in environmental monitoring, industrial automation, infrastructure health monitoring, and other fields.

[0003] Most traditional Φ-OTDR systems use a purely electrical signal processing method, which has many shortcomings:

[0004] First, traditional purely electrical signal processing requires converting optical signals into electrical signals. This process not only introduces additional noise but also makes the system extremely sensitive to electromagnetic interference. In environments with strong electromagnetic interference, such as those in the power and petrochemical industries, this sensitivity can easily lead to signal distortion or misjudgment, seriously impacting system stability and reliability.

[0005] Secondly, traditional purely electrical signal processing methods have bottlenecks in high-precision signal acquisition and are difficult to effectively suppress noise, resulting in limited dynamic range and strain resolution of the system, which cannot meet the needs of high-precision monitoring.

[0006] In addition, the electronic components in the pure electrical domain signal processing system are more sensitive to environmental conditions and are easily affected by factors such as temperature and humidity, making it difficult to ensure the long-term stability of the system in complex environments and increasing maintenance costs.

[0007] In terms of data processing speed, the data processing rate of the Φ-OTDR system is limited by optoelectronic conversion and complex signal processing processes, and is usually unable to meet the needs of large-scale, real-time monitoring. Summary of the Invention

[0008] Objectives of the invention: The first objective of the present invention is to address the problems of slow data processing speed, weak anti-electromagnetic interference capability, and poor environmental adaptability in the prior art, and to provide a partially all-optical signal processing method for phase-sensitive optical time-domain reflectometry. The second objective of the present invention is to provide a partially all-optical signal processing system for phase-sensitive optical time-domain reflectometry.

[0009] Technical solution: The present invention provides a partial all-optical signal processing method for a phase-sensitive optical time-domain reflectometer, comprising:

[0010] Get the phase to be demodulated The backscattered Rayleigh signal;

[0011] The amplified and filtered Rayleigh backscattered signal is divided into N optical signals according to a certain ratio, N ≥ 2;

[0012] Performing a derivative operation on N-1 optical signals among the N optical signals, and performing a delay operation on the remaining optical signal to keep it synchronized with the derivative-operated N-1 optical signal;

[0013] Performing synchronous photoelectric detection on the N-1 optical signals subjected to the derivative operation and the 1 optical signal subjected to the delay operation to obtain the optical power of the N optical signals;

[0014] Determined based on the optical power of N optical signals The phase to be demodulated The derivative of Perform Fourier transform and divide by iω to get frequency domain information; i is the imaginary unit, and ω is the frequency of the light wave.

[0015] Furthermore, when the backscattered Rayleigh scattering signal E0(t) is divided into two optical signals E1 and E2, the optical signal E1 is subjected to a derivative operation and photoelectric detection to obtain the optical power I1, and the optical signal E2 is subjected to a delay operation and photoelectric detection to obtain the optical power I2; the phase derivative is calculated from the optical powers I1 and I2. The formula is as follows:

[0016]

[0017] Among them, I0 is a DC signal.

[0018] Furthermore, when the backscattered Rayleigh scattering signal E0(t) is divided into three optical signals E4, E5 and E6, the optical signals E4 and E5 are subjected to derivative operation and photoelectric detection to obtain the corresponding optical powers I4 and I5, and the optical signal E6 is subjected to delay operation and photoelectric detection to obtain the optical power I6; the phase derivative is calculated from the optical powers I4, I5 and I6 The formula is as follows:

[0019]

[0020] Among them, I0 is a DC signal.

[0021] The present invention provides a partial all-optical signal processing system for a phase-sensitive optical time-domain reflectometer, comprising:

[0022] The second erbium-doped fiber amplifier is used to demodulate the phase Amplify the backscattered Rayleigh signal;

[0023] The second DWDM is used to filter the amplified Rayleigh backscattered signal;

[0024] A coupling unit is used to divide the amplified and filtered Rayleigh backscattered signal into N optical signals according to a certain ratio, where N is greater than or equal to 2;

[0025] an all-optical signal processing unit, configured to perform a derivative operation on N-1 optical signals among the N optical signals, and perform a delay operation on the remaining optical signal to keep it synchronized with the derivative-operated N-1 optical signal;

[0026] Photoelectric detectors, used to synchronously perform photoelectric detection on the N-1 optical signals subjected to the derivative operation and the 1 optical signal subjected to the delay operation, to obtain the optical power of the N optical signals; the number of photoelectric detectors is equal to the number of N optical signals and they correspond one to one;

[0027] A data acquisition card is used to receive the optical power of N optical signals acquired by each photoelectric detector;

[0028] PC is used to determine the optical power of N optical signals The phase to be demodulated The derivative of ; and Perform Fourier transform and divide by iω to get frequency domain information; i is the imaginary unit, and ω is the frequency of the light wave.

[0029] Furthermore, the coupling unit uses a 10:90 coupler, and the backscattered Rayleigh signal is divided into two optical signals E1 and E2.

[0030] Furthermore, the all-optical signal processing unit includes an optical delay device and an optical derivation device, and the optical derivation device is used to perform a derivation operation on the optical signal E1 to obtain E1 ′ The optical delay device is used to delay the optical signal E2; the two photodetectors are used to delay E1 respectively. ′ The optical power I1 and I2 are obtained by photoelectric detection of the delayed optical signal E2; the phase derivative is calculated from the optical power I1 and I2. The formula is as follows:

[0031]

[0032] Among them, I0 is a DC signal.

[0033] Furthermore, the coupling unit uses a 50:50 coupler, a Mach-Zehnder interferometer and a 3×3 coupler connected in series, and the backscattered Rayleigh signal is divided into three optical signals E4, E5 and E6.

[0034] Furthermore, the all-optical signal processing unit includes an optical delay device and two optical derivation devices, and the two optical derivation devices are used to perform derivation operations on the optical signals E4 and E5 respectively to obtain E4 ′ 、E5 ′ The optical delay device is used to delay the optical signal E6; the three photodetectors are used to delay the optical signal E4. ′ 、E5 ′ The optical power I4, I5 and I6 are obtained by photoelectric detection of the delayed optical signal E6; the phase derivative is calculated from the optical power I4, I5 and I6. The formula is as follows:

[0035]

[0036] Among them, I0 is a DC signal.

[0037] Furthermore, the optical guidance device adopts a long-period fiber grating, a spatial light modulator, an on-chip integrated optical circuit, a photonic crystal device or a metasurface device.

[0038] Furthermore, the partial all-optical signal processing system for phase-sensitive optical time-domain reflectometry further includes a laser, a pulse signal generator, a signal modulator, a first erbium-doped fiber amplifier, a first DWDM, a circulator, and a sensing fiber;

[0039] The laser is used to emit continuous light with a wavelength of λ to the signal modulator; the pulse signal generator is used to emit a periodic pulse signal to drive the signal modulator; after receiving the periodic pulse signal sent by the pulse signal generator, the signal modulator is used to modulate the continuous light with a wavelength of λ emitted by the laser into a detection light pulse signal and send it to the first erbium-doped fiber amplifier for amplification; the first DWDM is used to filter the amplified detection light pulse signal; the circulator is used to transmit the amplified and filtered detection pulse signal to the sensing fiber, and transmit the backscattered Rayleigh scattering signal generated by the sensing fiber to the second erbium-doped fiber amplifier.

[0040] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the present invention realizes partial all-optical processing of optical signals by performing derivative and delay operations on multiple optical signals respectively, effectively alleviating the introduction of noise in the traditional electrical domain processing process, and significantly improving the signal-to-noise ratio and signal stability of the system. At the same time, the partial all-optical processing of optical signals simplifies the signal processing flow, can significantly reduce the time delay of signal processing, achieve a response speed of milliseconds, and meet the needs of large-scale, real-time monitoring. In addition, this technical means also has a certain anti-electromagnetic interference capability, can operate stably in a strong electromagnetic interference environment, has stronger adaptability to environmental conditions, can maintain long-term stable operation in harsh environments, and significantly reduces maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the structure of a partially all-optical signal processing system for directly detecting DAS (Distributed Acoustic Sensing) signals for a phase-sensitive optical time-domain reflectometer, provided in Example 2 of the present invention;

[0042] Figure 2 This is a timing flow chart of direct detection DAS signal processing for partial all-optical signal processing in Example 2 of the present invention;

[0043] Figure 3 4 is a schematic structural diagram of a partial all-optical signal processing system for a 3×3_DAS signal of a phase-sensitive optical time-domain reflectometer provided by embodiment 4 of the present invention;

[0044] Figure 4 This is a timing flow chart of 3×3_DAS signal processing for partial all-optical signal processing in Example 4 of the present invention;

[0045] Figure 5 This is a timing flow chart of full electrical domain data processing of 3×3_DAS signals in the prior art. DETAILED DESCRIPTION

[0046] The present invention will be further described below with reference to the accompanying drawings.

[0047] Example 1

[0048] Embodiment 1 provides a partial all-optical signal processing method for directly detecting a DAS signal (a signal obtained by a Φ-OTDR) for a phase-sensitive optical time domain reflectometer, comprising the following steps:

[0049] (1) Obtain the phase to be demodulated The backscattered Rayleigh signal.

[0050] Backward Rayleigh scattered signals are generated in the sensing fiber and outputted outwards through a circulator, which is a prior art. In Example 2, some components of the all-optical signal processing system will be introduced in detail.

[0051] Assume that the light field of the output backscattered Rayleigh signal is:

[0052]

[0053] Where A(t) is the amplitude of the light field, which is slowly varying and its derivative can be ignored when taking the derivative; ω is the frequency of the light wave, which is a constant; It is the phase change caused by external sound wave interference, that is, the phase to be demodulated.

[0054] (2) The amplified and filtered Rayleigh backscattered signal is divided into two optical signals E1 and E2 according to a certain ratio, which can be expressed as:

[0055]

[0056] (3) Perform a derivative operation on the optical signal E1 and a delay operation on the optical signal E2 to keep synchronization with the optical signal E1 after the derivative operation.

[0057] The derivative of the optical signal E1 is shown in formula (3):

[0058]

[0059] Where k is the coefficient; The phase to be demodulated The derivative of .

[0060] (4) Performing synchronous photoelectric detection on the optical signal E1 after the derivative operation and the optical signal E2 after the delay operation to obtain the optical powers I1 and I2 of the two optical signals.

[0061]

[0062] (5) Determine based on the optical power I1 and I2 of the two optical signals

[0063]

[0064] The DC signal I0 is generated because the light wave frequency ω is too high, which exceeds the response frequency range of the photodetector. As a result, the photodetector cannot effectively detect the high-frequency light wave and can only output a DC signal.

[0065] When a sine signal (or cosine signal) is differentiated in the time domain, a 90° phase difference is generated from the phase perspective, which is equivalent to multiplying the Fourier transform of the signal in the frequency domain by iω, where i is the imaginary unit. The derivative of After that, no points are needed to restore You can directly Storage. Since Fourier transform requires multiple repeated pulse measurements in the slow-varying time direction, the properties of Fourier transform can be used to obtain Assume that The Fourier transform of but The Fourier transform of is:

[0066]

[0067] Just Perform Fourier transform and divide by iω to get The frequency domain information of the signal (dividing by iω is manifested in the electrical domain as filtering out DC noise, which can improve the signal-to-noise ratio of the signal).

[0068] Example 2

[0069] Example 2 provides a partial all-optical signal processing system for directly detecting DAS signals (signals obtained by Φ-OTDR) for a phase-sensitive optical time domain reflectometer, which is used to implement the partial all-optical signal processing method for directly detecting DAS signals for a phase-sensitive optical time domain reflectometer described in Example 1.

[0070] like Figure 1 As shown, the partial all-optical signal processing system for directly detecting DAS signals for phase-sensitive optical time-domain reflectometry includes: a laser, a pulse signal generator, a signal modulator, a first erbium-doped fiber amplifier, a first DWDM (the DWDM is used as an optical filter), a circulator, a sensing fiber, a second erbium-doped fiber amplifier, a second DWDM, a coupling unit, an all-optical signal processing unit, a photodetector, a data acquisition card, and a PC (computer).

[0071] In this second embodiment, the coupling unit uses a 10:90 coupler, and the all-optical signal processing unit includes an optical delay device (FDD) and an optical derivative device. The optical derivative device can be, for example, a long-period fiber grating (LPFG), a spatial light modulator (SLM), an on-chip integrated optical circuit, a photonic crystal device, a metasurface device, etc.

[0072] The laser emits continuous light with a wavelength of λ to the signal modulator, and the pulse signal generator emits a periodic pulse signal to drive the signal modulator (which can be an acousto-optic modulator, an electro-optic modulator, an optical switch, etc.). After receiving the periodic pulse signal sent by the pulse signal generator, the signal modulator modulates the continuous light with a wavelength of λ emitted by the laser into a detection light pulse signal. The detection light pulse signal amplified by the first erbium-doped fiber amplifier and filtered by the first DWDM enters the sensing optical fiber (which can be a single-mode optical fiber, a few-mode optical fiber, a multi-core optical fiber, etc.) through the circulator port 1 and port 2, and the backscattered Rayleigh scattering signal generated in the sensing optical fiber is output through the circulator port 2 and port 3. This involves a phase shifter to be demodulated. The generation and output of the Rayleigh backscattering signal are prior arts.

[0073] Subsequently, the output backscattered Rayleigh signal is transmitted to the second erbium-doped fiber amplifier, which has a phase to be demodulated. The second DWDM performs a filtering operation on the amplified Rayleigh backscattered signal.

[0074] The amplified and filtered backscattered Rayleigh signal enters a 10:90 coupler, which outputs two optical signals, E1 and E2. One optical signal is derivatized by a long-period fiber grating (LPFG), while the other optical signal, E2, is delayed by an optical delay device (FDD). The signals are then received by two photodetectors (PDs) to obtain the optical powers I1 and I2 of the two optical signals.

[0075] The data acquisition card receives the optical power I1 and I2 obtained by the two photodetectors. The PC determines the optical power I1 and I2 of the two optical signals. And Perform Fourier transform and divide by iω to get Frequency domain information; i is the imaginary unit, ω is the frequency of the light wave, The phase to be demodulated The derivative of .

[0076] Assume that the light field of the output backscattered Rayleigh signal is:

[0077]

[0078] Where A(t) is the amplitude of the light field, which is slowly varying and its derivative can be ignored when taking the derivative; ω is the frequency of the light wave, which is a constant; It is the phase change caused by external sound wave interference, that is, the phase to be demodulated.

[0079] E0(t) is split into two paths after passing through a 90:10 coupler. The optical field signals output from the two paths of the coupler can be expressed as:

[0080]

[0081] The signal processing process inside the all-optical signal processing unit is as follows: Figure 2 As shown, Figure 2 The optical signal calculation process in MATLAB mainly realizes the signal differentiation and optical delay mathematically.

[0082] After two optical signals E1 and E2 enter the all-optical signal processing unit, E1 enters the optical derivation device, and the derivation result is shown in Equation (3). It then enters photodetector 1 (PD1), where the optical power obtained is I1. E2 passes through a fiber delay device (FDD) and is detected by photodetector 2 (PD2), where the optical power obtained is I2. The function of the optical delay device is to ensure that the delayed optical signal and the other optical signals arrive at the corresponding photodetector at the same time. The output results I1 from PD1 and I2 from PD2 are shown in Equation (4).

[0083]

[0084] Where k is the coefficient; The phase to be demodulated The derivative of .

[0085]

[0086] After the above two signals are collected by the data acquisition card, they are squared and DC removed to obtain Signal, It is expressed as follows:

[0087]

[0088] The DC signal I0 is generated because the light wave frequency ω is too high, which exceeds the response frequency range of the photodetector. As a result, the photodetector cannot effectively detect the high-frequency light wave and can only output a DC signal.

[0089] When a sine signal (or cosine signal) is differentiated in the time domain, a 90° phase difference is generated from the phase perspective, which is equivalent to multiplying the Fourier transform of the signal in the frequency domain by iω, where i is the imaginary unit. The derivative of After that, no points are needed to restore You can directly Storage. Since Fourier transform requires multiple repeated pulse measurements in the slow-varying time direction, the properties of Fourier transform can be used to obtain Assume that The Fourier transform of but The Fourier transform of is:

[0090]

[0091] Just Perform Fourier transform and divide by iω to get The frequency domain information of the signal (dividing by iω is manifested in the electrical domain as filtering out DC noise, which can improve the signal-to-noise ratio of the signal).

[0092] Long-period fiber grating (LPFG) achieves modulation (derivation) of the optical signal by periodically modulating the refractive index to couple the core mode with the cladding mode. When the optical signal passes through the long-period fiber grating, the optical energy in the core is partially coupled to the cladding mode and gradually lost during transmission. This mode coupling characteristic causes the power of the optical signal to change near the resonant wavelength, thereby forming a loss peak in the transmission spectrum. The transmission spectrum of the long-period fiber grating can be regarded as a band-stop filter. By designing the structural parameters of the grating (such as grating period, length, coupling coefficient, etc.), the transmission spectrum of the grating can be made to meet the response function required by the differentiator. Under full coupling conditions, the amplitude function curve of the core response function of the long-period fiber grating is approximately linear near the resonant wavelength, and the phase undergoes a π jump at the center frequency. This characteristic is consistent with the response function of a first-order differentiator, that is:

[0093] H co (ω)∝j(ω opt -ω0)(7)

[0094] Among them, ω opt is the optical frequency, ω0 is the center frequency, and j is the imaginary unit.

[0095] Through this characteristic, long-period fiber gratings can realize the derivation operation of optical signals.

[0096] Example 3

[0097] Embodiment 3 provides a partial all-optical signal processing method for a 3×3_DAS signal of a phase-sensitive optical time-domain reflectometer, comprising the following steps:

[0098] (1) Obtain the phase to be demodulated The backscattered Rayleigh signal.

[0099] The backscattered Rayleigh scattering signal is generated in the sensing optical fiber and outputted outward through the circulator. This is an existing technology and will not be described in detail here.

[0100] Assume that the light field of the output backscattered Rayleigh signal is:

[0101]

[0102] Where A(t) is the amplitude of the light field, which is slowly varying and its derivative can be ignored when taking the derivative; ω is the frequency of the light wave, which is a constant; is the phase change caused by external sound wave interference, that is, the phase to be demodulated. Formula (8) and formula (1) are two different expressions of the same formula.

[0103] (2) The amplified and filtered Rayleigh backscattered signal is divided into three optical signals E4, E5, and E6 according to a certain ratio, which can be expressed as:

[0104]

[0105] Here, Δ represents the phase difference.

[0106] (3) Derivative operations are performed on the optical signals E4 and E5 respectively, and a delay operation is performed on the optical signal E6 to keep it synchronized with the optical signals E4 and E5 that have undergone the derivative operations.

[0107] The derivative results of optical signals E4 and E5 are shown in formula (11):

[0108]

[0109] in, The phase to be demodulated The derivative of .

[0110] (4) Performing synchronous photoelectric detection on the optical signals E4 and E5 after the derivative operation and the optical signal E6 after the delay operation to obtain the optical powers I4, I5, and I6 of the three optical signals.

[0111]

[0112] in, It is the phase difference caused by optical fiber strain caused by external interference such as sound (or vibration).

[0113] (5) Determine based on the optical power I4, I5, and I6 of the three optical signals

[0114] Accurately control the value of the phase difference Δ so that I4 = I5 and the coefficient is equal to I6, then:

[0115]

[0116] The DC signal I0 is generated because the light wave frequency ω is too high, which exceeds the response frequency range of the photodetector. As a result, the photodetector cannot effectively detect the high-frequency light wave and can only output a DC signal.

[0117] Similarly, just Perform Fourier transform and divide by iω to get The frequency domain information of the signal (dividing by iω is manifested in the electrical domain as filtering out DC noise, which can improve the signal-to-noise ratio of the signal).

[0118] Example 4

[0119] Embodiment 4 provides a partial all-optical signal processing system for 3×3_DAS signals of a phase-sensitive optical time-domain reflectometer, which is used to implement the partial all-optical signal processing method for 3×3_DAS signals of a phase-sensitive optical time-domain reflectometer described in embodiment 3.

[0120] like Figure 3 As shown, the partial all-optical signal processing system for 3×3_DAS signals for phase-sensitive optical time-domain reflectometry is basically the same as the partial all-optical signal processing system for directly detecting DAS signals for phase-sensitive optical time-domain reflectometry described in Example 2, except that:

[0121] The coupling unit adopts a series-connected 50:50 coupler, a Mach-Zehnder (MZI) interferometer and a 3×3 coupler. The all-optical signal processing unit includes an optical delay device FDD and two optical derivative devices.

[0122] The amplified and filtered backscattered Rayleigh signal enters the 50:50 coupler, Mach-Zehnder interferometer and 3×3 coupler in turn. The 3×3 coupler outputs three optical signals E4, E5 and E6 and sends them to the all-optical signal processing unit. In the all-optical signal processing unit, two long-period fiber grating LPFGs (spatial light modulators, on-chip integrated optical circuits, photonic crystal devices, metasurface devices, etc. can also be used) are used to perform derivative operations on the optical signals E4 and E5 respectively. The other optical signal E6 is delayed by the optical delay device FDD and then received by three photodetectors (PD) to obtain the optical powers I4, I5 and I6 of the three optical signals. The data acquisition card receives the optical powers I4, I5 and I6 obtained by the three photodetectors. The PC determines the optical powers of the three optical signals based on the optical powers. And Perform Fourier transform and divide by iω to get Frequency domain information; i is the imaginary unit, ω is the frequency of the light wave, The phase to be demodulated The derivative of .

[0123] Assume that the light field of the output backscattered Rayleigh signal is:

[0124] E0(t)=A(t)e i(ωt+(t)) (8)

[0125] Where A(t) is the amplitude of the light field, which is slowly varying and its derivative can be ignored when taking the derivative; ω is the frequency of the light wave, which is a constant; is the phase change caused by external sound wave interference, that is, the phase to be demodulated. Formula (8) and formula (1) are two different expressions of the same formula.

[0126] After passing through a 50:50 coupler, E0(t) enters the MZI interferometer. One arm of the MZI interferometer has a fixed phase difference Δ relative to the other arm. The optical field signals output by the two arms of the MZI interferometer are shown in Equation (10):

[0127]

[0128] Then, the optical fields of the three optical signals E4, E5 and E6 output by the 3×3 coupler at the end of the MZI interferometer are:

[0129]

[0130] The key steps are to use an all-optical signal processing solution. The internal signal processing process of 3×3_DAS is as follows: Figure 4 As shown, Figure 4 The optical signal calculation process in MATLAB mainly realizes the signal differentiation and optical delay mathematically. Figure 5 The steps described are electrical processing steps, which involve multiple calculations such as summation, subtraction, squaring, differentiation, and integration. Compared with electrical processing, using an all-optical signal processing solution can greatly reduce the amount of calculations.

[0131] When the three optical signals E4, E5, and E6 enter the all-optical signal processing unit, E4 and E5 enter two optical derivative devices respectively, and the derivative results are shown in formula (11). They then enter photodetector 1 (PD1) and photodetector 2 (PD2), respectively, and the optical powers obtained are I4 and I5. E6 passes through an optical delay device (Fiber Delay Devices, FDD) and is detected by photodetector 3 (PD3), and the optical power obtained is I6. The function of the optical delay device is to ensure that the delayed optical signal and the other optical signals arrive at the corresponding photodetector at the same time. The results of I4, I5, and I6 are shown in formulas (12) and (13). The ratio of the derivative result I4+I5 to 2I6 is the square of the sum of the phase derivative and the DC term, as shown in formula (14). After taking the square root of formula (14) and removing the DC term, the derivative of the phase change along the optical fiber is obtained, as shown in formula (15). After data acquisition, the phase derivative information and position information of the acoustic wave signal can be intuitively obtained from the display. If the frequency information of the acoustic wave is required, a Fourier transform can be performed in the electrical domain. After the phase derivative is transformed by FFT, the vibration position, vibration frequency and vibration amplitude along the optical fiber can be obtained.

[0132]

[0133] in, The phase to be demodulated The derivative of .

[0134]

[0135] in, It is the phase difference caused by optical fiber strain caused by external interference such as sound (or vibration).

[0136] The phase difference Δ between one arm of the MZI and the other arm is precisely controlled so that I4 = I5 and the coefficient is equal to I6. Then:

[0137]

[0138] The DC signal I0 is generated because the light wave frequency ω is too high, which exceeds the response frequency range of the photodetector. As a result, the photodetector cannot effectively detect the high-frequency light wave and can only output a DC signal.

[0139] Similarly, just Perform Fourier transform and divide by iω to get The frequency domain information of the signal (dividing by iω is manifested in the electrical domain as filtering out DC noise, which can improve the signal-to-noise ratio of the signal).

[0140] This invention replaces traditional all-electrical data processing with partial all-optical signal processing during DAS signal processing, significantly improving the system's data processing speed and enabling rapid processing of distributed fiber-optic sensing signals. Furthermore, it offers significant advantages and competitiveness in reducing costs, making it of great significance for practical application and promotion.

Claims

1. A partial all-optical signal processing method for phase-sensitive optical time-domain reflectometry, characterized in that: include: Get the phase to be demodulated The backscattered Rayleigh signal; The amplified and filtered Rayleigh backscattered signal is divided into N optical signals according to a certain ratio, N ≥ 2; Performing a derivative operation on N-1 optical signals among the N optical signals, and performing a delay operation on the remaining optical signal to keep it synchronized with the derivative-operated N-1 optical signal; Performing synchronous photoelectric detection on the N-1 optical signals subjected to the derivative operation and the 1 optical signal subjected to the delay operation to obtain the optical power of the N optical signals; Determined based on the optical power of N optical signals The phase to be demodulated The derivative of Perform Fourier transform and divide by iω to get frequency domain information; i is the imaginary unit, and ω is the frequency of the light wave.

2. The partial all-optical signal processing method for phase-sensitive optical time-domain reflectometry according to claim 1, characterized in that: When the backscattered Rayleigh scattering signal E0(t) is divided into two optical signals E1 and E2, the optical signal E1 is subjected to a derivative operation and photoelectric detection to obtain the optical power I1, and the optical signal E2 is subjected to a delay operation and photoelectric detection to obtain the optical power I2; the phase derivative is calculated from the optical powers I1 and I2 The formula is as follows: Among them, I0 is a DC signal.

3. The partial all-optical signal processing method for phase-sensitive optical time-domain reflectometry according to claim 1, characterized in that: When the backscattered Rayleigh scattering signal E0(t) is divided into three optical signals E4, E5 and E6, the optical signals E4 and E5 are subjected to derivative operation and photoelectric detection to obtain the corresponding optical powers I4 and I5, and the optical signal E6 is subjected to delay operation and photoelectric detection to obtain the optical power I6; the phase derivative is calculated from the optical powers I4, I5 and I6 The formula is as follows: Among them, I0 is a DC signal.

4. A partially all-optical signal processing system for a phase-sensitive optical time-domain reflectometer, characterized in that: include: The second erbium-doped fiber amplifier is used to demodulate the phase Amplify the backscattered Rayleigh signal; The second DWDM is used to filter the amplified Rayleigh backscattered signal; A coupling unit is used to divide the amplified and filtered Rayleigh backscattered signal into N optical signals according to a certain ratio, where N is greater than or equal to 2; an all-optical signal processing unit, configured to perform a derivative operation on N-1 optical signals among the N optical signals, and perform a delay operation on the remaining optical signal to keep it synchronized with the derivative-operated N-1 optical signal; a photoelectric detector for synchronously performing photoelectric detection on the N-1 optical signals subjected to the derivative operation and the 1 optical signal subjected to the delay operation, so as to obtain the optical power of the N optical signals; The number of photoelectric detectors is equal to the number of N optical signals and they correspond one to one; A data acquisition card is used to receive the optical power of N optical signals acquired by each photoelectric detector; PC is used to determine the optical power of N optical signals The phase to be demodulated The derivative of ; and Perform Fourier transform and divide by iω to get frequency domain information; i is the imaginary unit, and ω is the frequency of the light wave.

5. The partially all-optical signal processing system for phase-sensitive optical time-domain reflectometry according to claim 4, characterized in that: The coupling unit uses a 10:90 coupler, and the backscattered Rayleigh signal is divided into two optical signals E1 and E2.

6. The partially all-optical signal processing system for phase-sensitive optical time-domain reflectometry according to claim 5, characterized in that: The all-optical signal processing unit includes an optical delay device and an optical derivation device. The optical derivation device is used to perform a derivation operation on the optical signal E1 to obtain E1 ′ ; The optical delay device is used to delay the optical signal E2; Two photoelectric detectors are respectively ′ The optical power I1 and I2 are obtained by photoelectric detection of the delayed optical signal E2; the phase derivative is calculated from the optical power I1 and I2. The formula is as follows: Among them, I0 is a DC signal.

7. The partially all-optical signal processing system for phase-sensitive optical time-domain reflectometry according to claim 4, characterized in that: The coupling unit adopts a 50:50 coupler, a Mach-Zehnder interferometer and a 3×3 coupler connected in series, and the back Rayleigh scattering signal is divided into three optical signals E4, E5 and E6.

8. The partially all-optical signal processing system for phase-sensitive optical time-domain reflectometry according to claim 7, characterized in that: The all-optical signal processing unit includes an optical delay device and two optical derivative devices. The two optical derivative devices are used to perform derivative operations on optical signals E4 and E5 to obtain E′4 and E′5 respectively; the optical delay device is used to perform a delay operation on optical signal E6. The three photodetectors respectively detect E′4, E′5 and the delayed optical signal E6 to obtain the optical powers I4, I5 and I6. The phase derivative is calculated from the optical powers I4, I5 and I6. The formula is as follows: Among them, I0 is a DC signal.

9. The partially all-optical signal processing system for phase-sensitive optical time-domain reflectometry according to claim 6 or 8, characterized in that: The optical guidance device adopts a long-period fiber grating, a spatial light modulator, an on-chip integrated optical circuit, a photonic crystal device or a metasurface device.

10. The partially all-optical signal processing system for phase-sensitive optical time-domain reflectometry according to claim 4, characterized in that: It also includes a laser, a pulse signal generator, a signal modulator, a first erbium-doped fiber amplifier, a first DWDM, a circulator and a sensing fiber; The laser is used to emit continuous light with a wavelength of λ to the signal modulator; the pulse signal generator is used to emit a periodic pulse signal to drive the signal modulator; The signal modulator is used to modulate the continuous light with a wavelength of λ emitted by the laser into a detection light pulse signal after receiving the periodic pulse signal sent by the pulse signal generator, and send it to the first erbium-doped fiber amplifier for amplification; the first DWDM is used to filter the amplified detection light pulse signal; the circulator is used to transmit the amplified and filtered detection pulse signal to the sensing fiber, and transmit the backscattered Rayleigh scattering signal generated by the sensing fiber to the second erbium-doped fiber amplifier.

Images